Fix ordered dictionary bug.

[SalehHindi]

The add slice page fails to load because it tries to execute ordered(datasources) where datasources is a list of dictionaries. This PR fixes that bug and also adds to some tests that I wrote earlier that should have caught the page failing to load. My bad!

@ascott, this is the PR for the error I mentioned here.

[mistercrunch]

@ascott I'm wondering how it worked in your environment

[ascott]

@mistercrunch i am wondering the same thing. i tested locally and staging/prod and everything worked as expected.

@SalehHindi can you share the error that you are seeing?

[ascott]

maybe sorted sorts on a label key by default?

[ascott]

i opened a new PR to sort explicitly on the label key, and fixed the test name to be more clear.
#2939
@mistercrunch @SalehHindi

[SalehHindi]

So I just retested this and it looks like the add slice page works on python 2.7 but not 3.5. However, once you add key=lambda d: d["label"] as an argument to sorted like you did in your PR it does work on python 3.5.

For reference, this is the error I was seeing.

I'm going to close this PR because @ascott's solution is more concise than mine.